Romney's campaign got a much-needed shot in the arm two weeks ago when the Republican came out swinging in the first matchup between the two candidates, while Obama appeared passive and tongue-tied at times.
The strong debate performance helped Romney reverse his slide in the polls, and recent surveys put the race for the White House at a virtual dead heat just three weeks ahead of the Nov. 6 election.
In a Reuters/Ipsos daily tracking poll on Tuesday, Obama gained ground on Romney for the third straight day, leading 46 percent to 43 percent.
"I think you'll see somebody who will be strong, who will be passionate, who will be energetic, who will talk about ... not just the last four years but what the agenda is for the future and how we continue to move our economy forward," Obama's senior campaign adviser Robert Gibbs said on MSNBC.
The 90-minute debate at Hofstra University in New York begins at 9 p.m. EDT (0100 Wednesday GMT).
Both men will have to deal with the more intimate town hall format of Tuesday's debate, which often inhibits political attacks as the candidates focus on connecting with the voters asking the questions.
It also offers an element of uncertainty as the candidates cannot predict what the audience of undecided voters might ask, which could range from tax policy to job creation to foreign policy.
"Almost all of the pressure will be on Obama this time, given how poorly he performed in the first debate and how much that seemed to help Romney and change the race," said political scientist Andrew Taylor of North Carolina State University.
The town hall format lets the candidates "talk directly to people and look them in the eye and try to connect, which has not been a strength for either of them," Taylor said. "But you can still make strong points with a velvet glove."
During the first debate, Obama was widely criticized for not challenging Romney on exactly how he plans to give Americans a big tax cut without adding to the deficit, and for not calling attention to the more moderate views Romney appeared to present during the matchup.
A Gallup-USA Today poll published on Tuesday showed the two had similar favorable ratings from registered voters. But the survey showed Romney ahead of Obama by four percentage points among likely voters in the 12 battleground states.
The Reuters/Ipsos poll that gave Obama an edge showed the number of undecided voters had increased, indicating a drop of support for Romney among the coveted voting bloc.
The online survey of 1,846 likely voters was conducted between Oct. 12 and Oct. 16. The precision of the poll is measured using a credibility interval, which is plus or minus 2.6 percentage points for likely voters.
For Obama, trying to repair damage from the last debate, the challenge will be to confront Romney on the issues without seeming nasty or too personal.
Romney, a wealthy former private equity executive often accused of failing to connect with ordinary people, would be happy with a steady performance to keep up his momentum.
LINES OF ATTACK
The economy is expected to be a dominant topic. Obama is able to tout the latest jobs report, which showed that the unemployment rate unexpectedly dropped to 7.8 percent in September and reached its lowest level since Obama took office.
Romney has countered that the labor market is not healing fast enough.
Glenn Hubbard, one of Romney's top economic advisers, told Reuters on Tuesday that the Republican candidate was prepared to question Obama's record on the economy.
"His objective is to continue the conversation with voters about what the right economic policies are for the country," Hubbard said on the sidelines of an economic conference in New York.
"He did that really well last time and I'd be stunned if he doesn't do it well toReuters
Since the last debate, both sides have also focused on new lines of attack that are likely to come up on Tuesday.
Romney was expected to stay on the offensive over the administration's handling of diplomatic security in Libya before the attacks there that killed the US ambassador and three other Americans. The debate comes a day after Secretary of State Hillary Clinton assumed responsibility for the lack of security that failed to protect against the deadly attack.
"It's a matter of leadership; it's a matter of straight answers," Republican National Committee chairman Reince Priebus said on MSNBC. "I just get a feeling that this president hasn't been straight with the American people."
Democrats, hoping to make more inroads with women voters, have hit Romney and his running mate Paul Ryan for their opposition to abortion rights.
The Gallup poll highlighted the importance of women voters, who have traditionally preferred Obama. The poll showed Romney has pulled within one percentage point among likely women voters.
Obama and Romney have taken time off the campaign trail to prepare for the showdown, the second of three presidential debates. The final one will be next Monday, Oct. 22, in Boca Raton, Florida, and will focus on foreign policy issues.